1. Field of the Invention
The invention relates to an electric radiant heater with an active sensor for detecting the positioning of a cooking vessel or pot on a hotplate covering the radiant heater.
2. Background Art
Such sensors, known e.g. from DE 196 03 845 A1, are used for detecting whether and possibly where a cooking vessel is standing on the hotplate. The heating system is only activated when the cooking vessel is located thereon. This takes place on the one hand to avoid the wasting of energy when there are no cooking vessels on the hotplate and on the other prevents any danger of burning or destruction of articles by hot, open-running hotplates.
The sensor according to DE 196 03 845 A1 is constructed as a wire loop, which runs in a substantially round form between the heater and the hotplate. The setting down of a corresponding metallic cooking vessel brings about a change to the inductance of the sensor loop. This change is detected by an associated electronic means as the setting down of a cooking vessel. In the intended manner, the heating system can be activated independently thereof. Difficulties arise through the fitting of the sensor to the radiant heater. Problems also occur with the sensor weight, particularly in a falling weight test, in which the sensor can e.g. damage a glass ceramic plate as the cooking area.
The problem of the invention is to provide an aforementioned electric radiant heater in which the fitting of the sensor to the radiant heater is simplified and the latter has an improved construction.
This problem is solved by a radiant heater having an active sensor for detecting the position of a cooking vessel on a hotplate, for example a glass ceramic plate, in which the radiant heater is located in at least one heating zone and is connected to a control. The control comprises an inductive resonant circuit, wherein the hotplate covers the radiant heater. The sensor comprises electrically conductive material, is part of said inductive resonant circuit of aid control, is located in the vicinity of said heating zone and at least partly covers said heating zone. The sensor runs in a substantially linear manner and is constructed loopless. Advantageous developments of the invention appear in the subclaims and are described in greater detail hereinafter. By express reference the wording of the claims is made into part of the content of the present description. In the application, the word xe2x80x9ccomprisexe2x80x9d means xe2x80x9cincludingxe2x80x9d and is not limited to the meaning of xe2x80x9cconsistingxe2x80x9d.
Unlike in the known, conventional circular sensor loops or coils, the sensor according to the invention is constructed in loopless manner. It runs substantially linearly and preferably at least in essential parts of its path. Particular preference is given to it running substantially exclusively linearly in the vicinity of the radiant heater or the heating zone. In conjunction with the present invention loopless means that the sensor does not form a complete or a largely closed loop. In its path the sensor preferably bounds no surface.
The expression xe2x80x9csubstantially linearxe2x80x9d also means a not excessively undulating or similarly constructed sensor. Finally, it passes in a single direction or its path can be described thereby.
A sensor according to the invention has the advantage that the construction can be considerably simplified. A complete, circumferential loop, which in certain circumstances can also have several turns, is not fitted to the radiant heater and instead this only applies to straight portions thereof. They can e.g. be fixed with at least one end to the edge of the radiant heater or an insulation surrounding the latter. Looplike sensors also suffer from the disadvantage that the central zone of the radiant heater cannot be precisely established, because it is not directly traversed by the sensors. Due to the circumferential, looplike character thereof no portion can pass through this central area. However, no problem arises in guiding a straight sensor over said central area.
It has surprisingly proved possible with the invention, e.g. with two wires stretched in parallel over a multicircuit heater to detect both the setting down of a cooking vessel and also its size and even its position.
It also surprisingly been found that the sensor need only have a portion running over the heating zone, e.g. constructed as a straight, electric conductor. It can extend from one edge of the radiant heater to beyond its centre and preferably up to the other edge, such a sensor enclosing no surface. Surprisingly the function or detection precision is just as good as with the above-described, parallel conductors as sensors. As a function of the set switching threshold of an associated electronic system, it is possible to decide whether a cooking vessel has been set down or whether the cooking vessel or position is accepted.
Advantageously the sensor runs transversely over a heating zone or the entire radiant heater. It is advantageously possible, particularly with a sensor having a single conductor or portion, to use radiant heaters provided with a metal plate or disk substantially carrying or containing the radiant heater. The metal disk can be constructed as a return conductor or as a second connection for the sensor. This obviates the need for complicated, additional connection work. It has surprisingly been found that this does not impair the function of such a cooking vessel detection sensor. At at least one of its end regions, the sensor can be electrically insulated from the metal disk of the radiant heater. By said insulated end region, it is connected to a first electrical connection accessible from the outside. The other sensor end is directly or indirectly connected to the metal disk. In a particularly simple construction it is only necessary to fasten a second electrical connection at a random point of the metal disk in order to be electrically connected thereto.
According to a particularly preferred development, a connection possibility or a connecting plug for the sensor contains both connections in a connecting member. For this purpose in the vicinity of one sensor end the connection member can be fixed to the radiant heater or the metal disk. When using the metal disk as a return conductor or as a second electrical connection, it is very easily possible to tap the signal at a random point or to place the connection member very close to one sensor end.
Advantageously the sensor passes centrally over the heating area of the radiant heater, which ensures that a cooking vessel placed on the associated hot point covers the sensor in virtually any appropriate position and permits a detection. In the case of a radiant heater with several heating areas, the sensor can pass over more than one heating area and in particular over all the heating areas.
It is also possible for the sensor only to cover separated areas, so that the cooking vessel position is detected for said separated area. This is e.g. advantageous with laterally positioned additional heating means for elongated baking or frying devices or the like.
According to one variant of the present invention, it is possible to fit the sensor to the radiant heater in such a way that when the latter is installed it passes at a limited distance below a hotplate on which the radiant heater is installed. This small distance can be 0.1 to 10 mm and is preferably very small, namely a few {fraction (1/10)} mm. As a measure for this distance it is also possible to use the upper edge of an insulating plate or the like surrounding the radiant heater and which in the fitted state engages on the underside of the hotplate.
In a further development of the invention, at at least one of the ends of the sensor the latter can have a height adjustment, so that a desired distance or spacing can be precisely set. Such a height adjustment can e.g. have an elongated hole, preferably in a direction perpendicular to the radiant heater plane and located on said radiant heater. The sensor height can be adjusted along this elongated hole.
It is possible to construct the sensor in rigid manner, preferably as a thick wire or in tubular form. For a tubular sensor it is particularly appropriate to use a metal tube, which can be electrically insulated to the outside. In a variant of the invention the sensor can be combined with a rod regulator conventionally used for radiant heaters. The metallic outer tube of the rod regulator can form the sensor or can be used as an electric conductor for the same. This makes it possible to create a combined component requiring much lower installation costs.
Advantageously a conventionally used rod regulator can be fitted with a residual thermal contact on the radiant heater and can be designed as a sensor. If the residual thermal contact of the rod regulator is not required, the space made available in said regulator can be used as a connecting block for the sensor connection.
According to another possibility of the invention the sensor can have an elastic or flexible construction, e.g. in the form of a wire, braid or metal band. The latter can be stretched over at least one portion of the heating area and acquire the necessary stability through the stretching effect.
Within the scope of the invention spring means can be provided for compensating a thermally caused length change of the sensor. Alternatively or additionally the spring means can be used for mounting at least one end of the sensor and/or for maintaining tension and therefore the sensor shape. It must be borne in mind that if the sensor position plays a part, the spring means should be constructed in such a way that they permit a precise, position-defined fastening. The spring tension should be matched to the time/thermal expansion limit of the sensor material or the sensor cross-section. This makes it possible to ensure that the system sensor/spring means has an optimum mutual matching. The spring means is preferably constituted by a leaf spring, which in one variant of the invention can be punched or manufactured from the metal edge of the support disk for the radiant heater.
It is possible to fix or mount at least one end of the sensor on the radiant heater using spring means. The spring means can be electrically insulated against a metal disk for receiving the radiant heater. However, in particularly preferred manner the spring means are used for the electrical binding of the sensor to the metal disk, which is then used as the return conductor or the second electrical connection.
The sensor must have a non-scaling construction, so that it is permanently not attacked or damaged by the high temperatures in the heating zone. It is also advantageous if the sensor material has no Curie point, otherwise there could be falsifications of the measured results.
Additionally it is possible with the above-described, conventionally used rod regulator, to incorporate a precious metal temperature measuring resistor, e.g. in the form of a PT 100 or PT 1000. The precious metal temperature measuring resistor can be interchanged with the ceramic part of the rod regulator. The outer tube of the rod regulator can be constructed as a sensor and as a holder for the precious metal temperature measuring resistor.
Finally, the invention also covers a cooking area with several radiant heaters, in which at least one and preferably all the radiant heaters can be constructed in the above-described manner.
A necessary sensor electronics for evaluating sensor signals should obviously be present and can be constructed as is described e.g. in DE 196 03 845 A1, whose content is by express reference made into part of the content of the present description.